Light emitting diodes (LEDs) are gaining wide acceptance in a variety of area-illumination applications, for example, architectural lighting, residential illumination, industrial lighting, outdoor lighting, theatrical lighting and the like. Crystalline inorganic LEDs based on Gallium nitride (GaN) are a common type of LEDs utilized in such applications.
In comparison to conventional organic light emitting diodes (OLEDs), crystalline inorganic LEDs offer a number of advantages, including superior brightness, e.g., brightness in the range of 6900 klm/m2 for LED in comparison to about 10 klm/m2 for OLED, increased efficiency, e.g., 144 lm/W for LED in comparison to 60 lm/W for OLED, advantageous lifetime, e.g., 50,000 hours for LEDs versus 10,000 hours for a blue OLED, and a beneficially increased current density, e.g., 35 A/cm2 for an LED in comparison to about 10 mA/cm2 for an OLED.
However, organic light emitting diodes have some advantages in comparison to inorganic crystalline light emitting diodes. Organic LEDs may be constructed as an area light source, whereas crystalline inorganic LEDs are generally point sources, often rendering such LEDs unsuitable for, or requiring complex optics for, area lighting applications. In addition, crystalline inorganic LEDs generally require an epitaxial growth process, which is generally considered an expensive process, e.g., requiring high vacuum and long durations. Further, crystalline inorganic LEDs often require a lattice-matched single crystal substrate, e.g., sapphire or Silicon carbide, which are generally more expensive than other substrates, and may often have less desirable optical and/or thermal properties. Still further, even a slight mismatch in a crystal lattice or in a coefficient of thermal expansion (CTE) between a substrate and an epitaxial layer grown at high temperature may result in interfacial defects, dislocations and/or cracks, which may significantly lower the production yield. In contrast, organic LEDs are generally amorphous, do not require epitaxial growth and offer greater variety of substrate selection, lower material and manufacturing costs, and higher manufacturing throughput and yield.